Showing papers on "Phased array published in 1992"

Coded excitation system for improving the penetration of real-time phased-array imaging systems

Abstract: Based on an analysis of the inherent signal-to-noise ratio (SNR) in medical ultrasound imaging, SNR improvements of 15-20 dB are theoretically possible for real-time phased-array imagers using coded excitation. A very simple coded excitation for phased arrays based on the principles of 'pseudochirp' excitation and equalization filtering is described. This system is capable of SNR improvements of about 15 dB with range sidelobe levels acceptable for many medical imaging applications. Such improvements permit increased operating frequencies, and hence enhanced spatial resolution, for real-time array imagers. Both simulations and measurements are used to demonstrate the efficacy of the method. >

Radiation and scattering characteristics of microstrip antennas on normally biased ferrite substrates

Abstract: Radiation and scattering characteristics of microstrip antennas and arrays printed on ferrite substrates with a normal magnetic bias field are described. The extra degree of freedom offered by the biased ferrite can be used to obtain a number of novel characteristics, including switchable and tunable circularly polarized radiation from a microstrip antenna having a single feed point, dynamic wide-angle impedance matching for phased arrays of microstrip antennas, and a switchable radar cross section reduction technique for microstrip antennas. Results are obtained from full-wave moment method solutions for single microstrip antennas and infinite arrays of microstrip antennas. A cavity model solution for a circular patch antenna on a biased ferrite substrate is also presented, to aid in understanding the operation of these antennas. >

Polarization agility in an RF radiator module for use in a phased array

Abstract: A 90° coupling circuit cascaded with a pair of hybrid mode latchable phase shifters provides polarization agility for an RF radiator module of the type typically used in a phased array. For example, such radiator modules typically may utilize an active microwave integrated circuit (MIC), a monolithic microwave integrated circuit (MMIC) or a passive reciprocal hybrid mode element (RHYME) circuit. These circuits are arranged to provide duplex RF transmit/receive functions with controllable phase shifts at each radiator site in a phased array. By appropriately setting the two controllable phase shifters to different combinations of phase shifts (e.g., 0° and/or 90°) to a dual orthogonal mode radiator, different spatial polarizations for RF radiator transmit/receive functions can be defined. The radiator itself may include a square or circular waveguide including, in some cases, a reciprocal dielectric quarter-wave plate and a non-reciprocal ferrite quarter-wave plate. If a square waveguide is utilized, then 0°, 90° hybrid mode latchable phase shifters may be arranged on either side of a common ground plane with direct waveguide coupling into a septum polarizer waveguide section of the radiator element. A 90° Lange hybrid coupler also may be used by itself in conjunction with an electrically rotatable ferrite quarter-wave plate radiating element to achieve a certain degree of polarization agility.

Efficient synthetic aperture imaging from a circular aperture with possible application to catheter-based imaging

Abstract: Phased-array imaging, including complete dynamic focus, is explored for imaging using a circular aperture. Based on the constraints of catheter-based systems, an efficient synthetic aperture method has been developed for imaging using a single wire connection between the imaging array and external electronics. The method employs a highly sampled array with an element pitch small compared to the acoustic wavelength. On any given firing of the array, however, a large number of channels are electrically connected on both transmission and reception. From firing to firing, one element is dropped and one new element is included, in analogy to a classic linear array system. Using an optimal filtering approach for synthetic aperture reconstruction, a dynamically focused image exhibiting diffraction limited resolution is produced. The results of detailed simulations are presented demonstrating the capabilities of the method. In addition, the prospects for real-time implementation of the reconstruction are discussed. >

Optical dispersion technique for time-delay beam steering

Abstract: A simple technique for steering the microwave radiation beam of a phased-array antenna is proposed and analyzed. Chromatic dispersion in equal-length fibers is used.

Synthetic receive aperture imaging with phase correction for motion and for tissue inhomogeneities. I. Basic principles

Abstract: The use of a synthetic receive aperture (SRA) system to increase the resolution, of a phased-array imaging system severalfold, by utilizing the available number of parallel receiver channels to address a larger number of transducer elements through a multiplexer system, is considered. Recent studies indicate that transducers with a very large number of elements will improve the detectability of small or low contrast targets when adaptive focusing is used to compensate for the effects of acoustic velocity inhomogeneities in tissue. With the effectively increased transducer element count afforded by an SRA system, a 1-by-N phased array could be split into an M-by-N array in order to improve resolution in the elevation dimension. Simulation results illustrate the lateral resolution achievable with several types of imaging systems: SRA, synthetic focus, and conventional phased array. Simulated images demonstrate the improvement in contrast resolution achievable using SRA. Experimental results show the improvement in beam width achieved by an experimental SRA system. >

Basic array theory

Abstract: Basic antenna array theory is outlined with major emphasis on pattern analysis and synthesis for periodic linear and planar arrays, phased arrays, and conformal arrays. Extension is made to synthesis techniques which use computer algorithms. These include arbitrary sidelobe control, shaped beams, and phase-only null steering. The subjects of random errors and phased array quantization errors are outlined. >

Finite phased array of microstrip patch antennas: the infinite array approach

Abstract: An efficient method of analysis of large infinite arrays based on a convolution technique that allows one to obtain the finite array characteristics from the infinite array results is presented. The edge effects are taken into account by convoluting the infinite array results with the proper current amplitude window on the array. The method is based on the use of Poisson's sum formula in the case of finite arrays applied here to microstrip antennas. It is an approximate technique that can be assimilated into a perturbation method. >

Coherent optical monolithic phased-array antenna steering system

Abstract: An optical-based RF beam steering system for phased-array antennas comprising a photonic integrated circuit (PIC). The system is based on optical heterodyning employed to produce microwave phase shifting by a monolithic PIC constructed entirely of passive components. Microwave power and control signal distribution to the antenna is accomplished by optical fiber, permitting physical separation of the PIC and its control functions from the antenna. The system reduces size, weight, complexity, and cost of phased-array antenna systems.

Safe stopping distance detector, antenna and method

Abstract: An FM/CW radar system is disclosed for determining a safe stopping distance between a moving vehicle and a potential obstacle. The radar signal is modulated linearly over several slopes. A microstrip phased array transmit/receive antenna is also disclosed having a hybrid tap, corporate feed structure. Signals from the antenna are amplified and filtered, and passed through an analog to digital converter to a signal processor, which performs a Fast Fourier Transform on the signals to convert them from time domain data to frequency domain data. The frequency domain data is then used to solve target range and doppler equations, determine safe stopping distances, and sound or display alarms if the safe stopping distance has been violated. A sensitivity control adjusts for road conditions or operator reaction time variations.

High temperature co-fired ceramic integrated phased array packaging

Abstract: A phased array package using a cofired ceramic material system to integrate antenna elements and an hermetic multi-chip MMIC cavity into a single module to provide incorporation of microwave circuit geometries into a system which has been used in the prior art only for low frequency applications. The integration provides a package very similar to a conventional integrated circuit package with substantial cost reductions over the complicated microwave assemblies of the present art.

Generation and control of microwave signals by optical techniques

Abstract: Optical techniques for microwave signal generation and optical control of microwave devices are described. Optical generation of microwave signals to 35 GHz and above by coherent heterodyne was carried out by FM sideband injection locking of laser diodes and by offset frequency phase locking of solid state lasers. Applications of optically generated microwave signals including optical control of phased array radar and photodetector characterisation are discussed. Optical injection locking, phase control, and phase locking of microwave oscillators are also presented.

Adaptive focusing and nulling hyperthermia annular and monopole phased array applicators

Abstract: An RF hyperthermia phased array applicator uses adaptive nulling and focusing with non-invasive electric field probes (112) to control the electric field intensity at selected positions in and around a target body (106) to provide improved heating of solid tumors (107) during hyperthermia treatment A gradient search or matrix inversion algorithm is used to control the amplitude and phase weighting for the phased array transmit elements (104) of the hyperthermia applicator A 915 MHz monopole phased array hyperthermia applicator for heating brain tumors has an enclosed vessel including a plurality of monopole transmit antenna elements disposed as a circular arc array on a ground plane which has an aperture for positioning the tumor in proximity to the monopole antenna elements Adaptive focusing with non-invasive electric field probes is used to maximize the electric field at the tumor site Parallel plate microwave waveguides are used to direct RF energy from the monopole phased array to the tumor site A microwave transmit and receive module generates amplitude and phase controlled transmit signals for exciting the monopole antenna elements, and receives passive microwave signals from the monopole antenna elements for taking non-invasive radiometry temperature measurements of the tumor site

Hybrid electronic fiber optic wavelength-multiplexed system for true time-delay steering of phased array antennas

Abstract: A hybrid electronic fiber optic true time-delay steering architecture is presented which retains the highly hardware compressive property of an earlier all-optical approach and introduces the economical advantages of electronics at every level possible without compromising overall performance. The architecture is particularly suited to large arrays where maximum advantage can be taken of the hardware compression. A detailed design based on this architecture is described for steering a linear, 16-element, L -band (0.7- to 1.4-GHz) array in transmit mode over a scan angle of ±20 deg with a delay resolution of 6 bits (0.63 deg). An analysis of the expected performance of the design is given together with progress toward the fabrication of the prototype system, which includes the first iteration electronic binary delay line subsystem and a single-segment, high-fidelity, directly modulated DFB laser diode fiber optic link. The experimental data from these modules is in agreement with the performance predicted from the analysis.

An NMR Phased Array for Human Cardiac 31P Spectroscopy

Abstract: A four-coil phased-array 31P NMR receiver was designed and tested for human cardiac applications, to determine whether the combination of relatively high signal-to-noise ratio (SNR) and large field of view produced in 1H imaging is also realized for in vivo31P spectroscopy. Spectra were acquired in parallel from an array of four overlapping 6.5-cm surface coils using one- and two-dimensional phase-encoding pulse sequences and were optimally combined to yield composite spectroscopic images. The phased array was found to generate useful 31P spectra from a 2.5-fold wider lateral region around the anterior myocardium than a single receiver of the same size as the array elements, with no increase in imaging time. In addition, the sensitive depth was increased by up to 2 cm over that of a single coil. Spectra could be acquired in roughly 15 min from a region extending to the middle of the heart, with voxel sizes of 2 X 2 X 4 cm3. For the average heart voxel, the SNR of the combined spectrum was higher than that of the best spectrum from any one coil in the array by 30%, with some voxels showing an increase as high as 60%.© 1992 Academic Press,Inc.

Laser radar system with phased-array beam steerer

Abstract: An optical beam steering device for use in a single-aperture laser transceiver system provides deflection of the transmitted and received beams in two planes, while maintaining the distinctive identities of each channel respective to their polarizations. The invention utilizes four single-dimensional beam deflecting devices, two for each orthogonal linear polarization of the two transceiver channels, one of these for each steering axis. In addition, a 90° polarization rotator and a quarter-wave plate are included in the arrangement of beam deflecting devices to satisfy the polarization requirements of these devices and of the transceiver channels. In a preferred embodiment, the beam deflecting devices comprise liquid crystal cells functioning as variable phase retarders, each of the cells comprising a first window having a common electrode, a second window having a multiplicity of electrodes in the form of electrically isolated, parallel stripes, and a layer of liquid crystal molecules intermediate the first and second windows. Means are provided for coupling a multiplicity of control signals individually between the multiplicity of stripe electrodes and the common electrode, thereby creating selectable local variations of refractive index in the liquid crystal layer.

Source identification system for closely separated spatial sources

Abstract: A phased array source identification receives signals from remote sources and determines direction of arrival angles and the respective powers of coherent electromagnetic signals for the purpose of spatial localization and identification of relatively low power coherent sources in the presence of other coherent sources of relatively large signal power. The system employs covariant analysis of the received signals followed by eigenanalysis to produce eigenvectors and eigenvalues. A superresolution algorithm creates array manifold vectors corresponding to source direction of arrival, that lie in the signal subspace of the eigenvectors. In radar applications low power sources correspond to targets, while the high power sources would correspond to jammers. The relative power of radar echoes contribute information relevant to the identification of real sources as opposed to false alarms. Other applications may include cellular telephone systems and sonar systems.

Resolution enhancement for ultrasonic reflection mode imaging

Abstract: An annular array scanner utilizes a synthetic focusing approach to improve imaging results. Image sharpening methods include corrections for the speed of sound of the image, phased array misregistration and separate view misalignment as well as inverse filtering for the scanning system point spread function.

Integrated horn antennas for millimeter-wave applications

Abstract: The development of integrated horn antennas since their introduction in 1987 is reviewed. The integrated horn is fabricated by suspending a dipole antenna, on a thin dielectric membrane, in a pyramidal cavity etched in silicon. Recent progress has resulted in optimized low- and high-gain designs, with single and double polarization for remote-sensing and communication applications. A full-wave analysis technique has resulted in an integrated antenna with performance comparable to that of waveguide-fed corrugated-horn antennas. The integrated horn design can be extended to large arrays, for imaging and phased-array applications, while leaving plenty of room for the RF and IF processing circuitry. Theoretical and experimental results at microwave frequencies and at 90 GHz, 240 GHz, and 802 GHz are presented. >

Acoustical evaluation of a prototype sector-vortex phased-array applicator

Abstract: A prototype sector-vortex phased-array applicator for ultrasound hyperthermia was constructed and acoustically evaluated. The array transducer consists of special lead-titanate ceramic elements of 16 sectors and two tracks attached on a element is driven by a complementary pair of power MOSFETs at 750 kHz. An annular focal field approximated by the Mth order Bessel function is theoretically predicted to be formed when the array elements are driven with a phase distribution that rotates M ( >

Pelvic imaging with phased-array coils: quantitative assessment of signal-to-noise ratio improvement.

Abstract: The signal-to-noise ratios (S/Ns) of two different pelvic magnetic resonance (MR) imaging phased arrays were compared with that of the body coil. Each array consisted of two coils placed anteriorly and two posteriorly, oriented transversely in one array and longitudinally in the other. S/N measurements were obtained in an adjustable water-filled phantom that stimulated the shape and radio-frequency loading effects of various-size patients. Depending on the simulated anterior-posterior thickness of the patient, the S/N produced by the longitudinal array ranged from 2.3 to 3.1 times higher than that of the body coil. The S/N of the transverse array was 3.1 to 3.4 times higher. The increased coil sensitivity permits imaging with shorter acquisition times, smaller fields of view, finer resolution, and/or thinner sections. Two examples in patients demonstrate the enhanced imaging capability of the phased arrays.

Integrated 6-bit photonic true-time-delay unit for lightweight 3-6 GHz radar beamformer

Abstract: The authors have developed a low-loss integrated 6-bit photonic time-delay unit to be used in the demonstration of a photonic beamformer for eight subarrays of a 3-6 GHz phased array radar. The current architecture for the electronic true-time-delay beamformer, and the proposed architecture for the equivalent photonic true-time-delay beamformer are presented. The 6-bit photonic time-delay unit design, showing the four 4*4 crossbar switch arrays realized using two 3-in LiNbO/sub 3/ substrates, is outlined. The time-delay unit fabrication is discussed. The results of the insertion loss and crosstalk measurements for each of sixty-four paths through the photonic time-delay unit are presented. >

Multiport scattering analysis of general multilayered printed antennas fed by multiple feed ports. I. Theory

Abstract: A general solution is given for a class of printed antenna geometries composed of multiple dielectric layers or ground planes, radiating patches, dipoles, or slots, and an arbitrary configuration of multiple transmission lines proximity-coupled or aperture-coupled to the radiating elements. The solution uses a full-wave spectral-domain moment method approach, and a new generalized multiport scattering formulation to model the excitation from the multiple feed lines. This method treats infinite phased arrays as well as isolated elements. The general theory using the new multiport scattering formulation is elaborated, with details of the key analytical and numerical aspects. Considering the unified nature of the multiport scattering analysis, and its simplicity, this analysis is appropriate for computer simulation of a large variety of multilayered microstrip antennas involving radome layers, dual polarized feeds, proximity-coupled or aperture-coupled elements, multifeed stacked or parasitic patches, and several related configurations for integrated phased array applications. >

A self-steering array for the SHARP microwave-powered aircraft

Abstract: SHARP (stationary high altitude relay platform) is a proposed airborne platform consisting of a light aircraft powered by microwave energy beamed to it from the ground. A design for a phased array which automatically tracks the aircraft as it flies on station is proposed. It uses a feedback link through the transmitted beam. Computer simulations are presented. >

Time-multiplexed phased-array antenna beam switching system

Abstract: An optical control system for a phased-array antenna system employs a time-multiplexed optical control architecture to provide very fast (a few hundred beams per second) antenna beam scanning using slow (milliseconds) response spatial light modulators in two optical signal processing channels. In each channel a cascade of relatively slow switching speed nematic liquid crystal cell spatial light modulators and associated free space delay units or fiber optic delay cables are disposed to receive transmit or receive optical input signals comprising a plurality of light beams. The control voltages applied to the spatial light modulators determine the paths of the light beams through the cascade and the differential time delay imparted to the light beams in the input optical signal. High speed 90° polarization rotators control the polarization of the transmit and receive optical input signals and the polarization of optical signals passing from the cascade, allowing for selecting the active channel and the transmit or receive mode of the active channel, thus enabling sequential rapid beam scans of the radar with a relatively short dead time between respective transmit/receive sequences. The spatial light modulators in the non-active channel are reconfigured during the dwell time of the active channel to set up for the next transmit/receive sequence.

Self-focusing antenna array

Abstract: A phased array for transmitting to a microwave powered aircraft is focussed and steered by feedback from the aircraft. Each antenna of the array is phase modulated in turn, and the resulting amplitude modulation of the field at the aircraft is used to calculate a correction to the antenna phase, which is telemetered back to the array system and applied to the antenna phase shifter.

Multiport scattering analysis of general multilayered printed antennas fed by multiple feed ports. II. Applications

Abstract: For Part I, see ibid., vol.40, no.5, p.469-481 (1992). The general analysis of part I is applied to several practical geometries of multilayer/multifeed printed antennas. These examples include a dual-feed circularly polarized geometry; a stacked patch geometry; a stripline-aperture coupled geometry with a radome; an open-end proximity-coupled patch; and dipole and slot geometries inclined or perpendicularly coupled to different feedlines. Features of the selected geometries cover many practical aspects of multilayer integrated phased arrays. Experimental results for several geometries are compared with the analytical results to demonstrate the accuracy and versatility of the analysis used. Various design considerations for the use of these multilayered printed antenna geometries in integrated phase array applications are discussed. >

Monolithic integrated optical time delay network for antenna beam steering

Abstract: A time delay network for phased array antenna beam steering employs a waveguide network as the delay element in a monolithic integration with other optical and electronic elements on a single substrate. A plurality of optical time delay stages are cascaded to form the delay network, with each stage having a selectable delay time. Each stage preferably has a reference or nominal time delay branch, and at least one other finite time delay branch. The lengths of the delay waveguides vary from stage to stage, permitting a high time delay resolution with a relatively small number of separate waveguides. The desired time delay is selected either by directing the modulated laser light into only one of the waveguide branches in each stage by means of waveguide switches or by splitting the light into all the waveguide branches of a stage and then activating only the detector connected to the desired delay waveguide. A variety of cascading schemes and waveguide layouts can be used to implement the time delay network.

Method and apparatus for calibrating phased array receiving antennas

Abstract: Disclosed is a method and apparatus for calibrating phased array receiving antennas that includes circuitry for generating a pair of calibration signals separable one from the other The signals are injected into the delay elements of the antenna from opposite ends of a complementary calibration cable The delay produced in the calibration signals is individually measured, and the delays summed and averaged to produce a delay measurement independent of delays produced by the calibration cable and accordingly delay measurement variations caused by environmental effects on the calibration cable

Direct computation of ultrasound phased-array driving signals from a specified temperature distribution for hyperthermia

Abstract: A method that obtains ultrasound hyperthermia applicator phased-array element driving signals from a desired temperature distribution is presented. The approach combines a technique which computes array element driving signals from focal point locations and intensities with a technique which calculates focal point locations and power deposition values from temperature requirements. Temperature specifications appear as upper and lower bounds within the tumor volume, and a focal point placement algorithm chooses focal patterns capable of achieving the temperature range objective. The linear algebraic structure of the method allows rapid calculation of both the phased-array driving signals and an approximate temperature field response. Computer simulations verify the method with a spherical section array (SSA) for a variety of temperature specifications and blood perfusion values. The scheme applies to any phased-array geometry. >